Treatment of hydrocarbons



Filed Deo. 24, 1948 NM. QW

QN. RN

Patented Apr. 17, 1951 .55,551

TREATMENT oF HYDRocARBoNs Kenneth M. Brown, Hinsdale, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application December 24, 1948, Serial No. 67,203

11 claims. 1

This invention relates to the treatment of hydrocarbons and more particularly to a combination of mutually related and interdependent steps comprising desulfurization of hydrocarbons and mercaptan decomposition of a selected fraction therefrom.'

A particularly eifective desulfurization process in commercial use at the present time is the Unisol process in which acidic organic compounds and particularly mercaptans are removed from gasoline by treatment with a caustic-methanol solution. In this process, a mercaptan fraction is separated from the other products, and in the present practice the mercaptan fraction is burned as fuel or otherwise disposed of. However, the mercaptan fraction contains valuable hydrocarbons, not only the hydrocarbons in solution in the mercaptans but also the hydrocarbon content of the mercaptan molecule and the present invention is directed to a novel method of recovering these hydrocarbons.

In a broad embodiment, the present invention relates to a combination process which comprises treating sour hydrocarbon oil with an alkali-solvent solution, separating a mercaptan fraction from said treating, subjecting said mercaptan fraction to decomposition to form hydrogen sulfide and hydrocarbon, and recovering said hydrocarbon.

In a specic embodiment the present invention relates to a combination process which comprises intimately contacting gasoline with caustic-methanol solution, separating treated gasoline from the caustic-methanol solution, regenerating said solution to separate an overhead fraction comprising mercaptans and methanol, separating a mercaptan fraction from a methanol fraction, subjecting said mercaptanfraction to high temperature treatment to form hydrogen sulfide and hydrocarbon, removing the hydrogen sulfide, and subjecting said hydrocarbon to contact with caustic-methanol solution.

While any suitable alkali reagent, including sodium hydroxide, potassium hydroxide, etc. and any suitable organic solvent which is more soluble in an aqueous solution of an alkali reagent than are hydrocarbons, including methanol, ethanol, propanol, acetone, ethylene glycol, glycol ethers, etc. may be used, the preferred treating reagent comprises an aqueous solution of sodium hydroxide or potassium hydroxide and methanol.

According to the present process, gasoline or fractions thereof containing acidic organiccompounds are treated with the alkali-solvent solution at a temperature above the freezing point returned for further use within the process.

of the solution. The preferred treating temperature is generally within the range of from about 80 to about 110 F., although in some cases lower or higher temperature may be used but theftemperature usually will not be below about V25"` and not above about 200 F. The pressure employed is usually within the range of from about 25 to about 200 pounds, although lower or higher pressures may be used in some cases.

As heretofore set forth, preferred treating reiagent comprises an aqueous solution of sodium hydroxide and methanol. The quantity of so dium hydroxide solution may range from about 0.5% to 10% or more by volume based ion the hydrocarbons to be treated, while the Vsodium hydroxide may be between about 35 and 50 Baume and preferably between about and about Baum. The methanol employed may be anhydrous or it may contain varying amounts of water. However, as the water content ci the methanol fraction increases, the concentration of the sodium hydroxide solution should be increased accordingly.

In accordance with the invention, gasoline containing mercaptans and usually. phenols is contacted with the caustic-methanol solution under the conditions hereinbefore set forth. Sodiummercaptides and phenolates are formed and are dissolved in the caustic-methanol solution. This solution is then separated from the hydrocarbons, the caustic-methanol being regenerated to convert the mercaptides into sodium hydroxide and mercaptans. The mercaptans, methanol and water are separated from the caustic and the latter is The mercaptans are separated from a water-alcohol mixture, usually by settling under carefully controlled conditions which avoid turbulence. The mercaptan fraction thus separated will contain varying amounts of hydrocarbons entrained therein. Further, the mercaptan itself com Vprises a chemical combination of hydrocarbons process in which the mercaptan fraction, alone or `in combination with other-fractions, is-,sub=

jected to conversion at a temperature sufficient to decompose the mercaptans to hydrogen sulfide and to thereby liberate hydrocarbons. Usually most refineries will employ some form of high temperature conversion and, in accordance with `a preferred embodiment of the'invention, the

ing the uidized process, the moving catalyst process, the slurry Ytype process, etc., wherein theV charge is intimately contacted -With the catalyst at a temperature of above aboutl'750F. Particularly suitable cracking catalysts comprise compositions of silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-magnesia, silicaalumina-zirconia, etc.

(2) Catalytic reforming process in `which the charge is contacted with a catalyst fostering dehydrogenation and aromatization as well as desulfurization reactions at a temperature above about 800 F. Similarly, this process may be either of the xedvbed or of the moving catalyst type. Particularly suitable catalysts for reforming processes include alumina-molybdena, alumina-chromia, etc., and the-reforming may be effected in the presence or absence of hydrogen.

(3) High temperature catalytic desulfurization process in which the charge is contacted with a suitable catalyst fostering conversion of mer- Ycaptans to hydrogen sulde at a temperature above about 500 F. but below about 800.and

preferably below about 750 F. This process may be effected in the presence or absence of hydrogen and usually will employ catalysts comprising alumina, bauxite, clay, nickel, nickel sulde, molybdenum sulfide, etc.

(4) Thermal cracking process in which the charge is converted in the absence of a'catalyst at a temperature above 800 F. and a pressure above 50 pounds per square inch, and generally at a temperature of'900 to 1050 F. and a pressure of 200 to 500 pounds.

. (5) Thermal reforming process in which the charge is'convertedin the absence of a catalyst at a` temperature usually within the range of about 950 to about l100 F, and at a pressure of from '100 to 1000 pounds. Decomposition of mercaptans into hydrogen sulfideand hydrocarbons also may be effected in the presence of hydrogen and hydrogenation cataof mercaptans may be effected at lowerk tempera'- tures. 1 Y

The invention is further illustrated in the accompanying diagrammatic flow drawing and the sodium sulde and is retained in the caustic solu- Y vents may be employed but not necessarily with equivalent results. Likewise, auxiliary equipment, such as valves, pumps, etc., have been omitted from the drawing in the interest of simplicity.

Referring to the drawing, the gasoline charging stock'to the process, which may comprise straight run gasoline, thermally cracked gasoline,`

v tic solution introducedto zone 2 through line 3,

whereby the-'hydrogen sulfide is converted into tion. In view of the fact that the caustic solution y containing sodium sulde cannot be regenerated by economical means, the caustic solution is preferably of low caustic concentration and generally will have a Baume gravity of from about 5 to about 15. The spent caustic is withdrawn from zone 2 through line' 4, while the gasoline substantially free from hydrogen sulde is withdrawn from zone 2 through line 5 and is directed through line 6 to mercaptan extraction zone 1. When the gasoline charged to the process does not contain hydrogen sulfide, it may be directed through lines i 8, 9 and 6 direct to extraction zone 1.

Extraction zone 'I may comprise one or a plurality of suitable extraction zones, Y preferably containing a suitablev packing material. The packing material should not be detrimentally affected by the caustic, methanol and hydrocarbons at the operating conditions prevailing in following description thereof. In the interest `of simplicity the following description will'be limited to the treatment of gasoline by means of a causticmethanol solution, although it is understood that other sour hydrocarbon fractions including burner or heater oils, fuel oil, lubricating oil, etc. and other Vsuitable alkali reagents and organic sol- Ywithdrawn from the process.

this Zone.A A particularly suitablepacking comprises carbon Raschig rings. Sodium hydroxide is introduced into the process through line I IJ and is directed through line I I into the upper portion of zone 1, preferably through a spray arrangement as indicated at I2. Usually suicient sodium hydroxide is recycled Within the process, in

the manner to be hereinafter set forth, and the sodium hydroxide introduced through line I0 from an extraneous source will comprise the makeup reagent to replace that lost or withdrawn from the process. Methanol is introduced to the process through line I3 and is directedthrough line I4 `at an intermediate point in zone l'. Here again the methanol will comprise primarily that recycled Within the process, in the manner to be hereinafterV set forth, and the methanol introduced through line I3 will comprise the makeup reagent to replace that lost or Although, in the case here illustrated, the caustic and methanol are introduced Kat different points to Zone 7, it is understood that in some cases the caustic and methanol may be commingled prior to introduction into zone 'I.

In zone 1, thegasoline passes upwardly in intimate contact with the caustic-methanol solution, and the acidic organic compounds,'such as mercaptans and phenols contained in the gasoline are converted into sodium mercaptides and phenolates. The rate of flow of thegasoline, causticl and methanol lare so adjusted that the treated gasoline being withdrawn from the upper portion of zone 'I through line I5 contains substantiallyV less mercaptans than the gasoline introduced through line 6. The treated gasoline may, if desired, be washed with Water or other` `Wise treated to remove methanol or traces of The mercaptides and phenolate's formed in zone 1 are dissolved in the caustic-methanol solution, and the caustic-methanol solution is withdrawn from the lower portion of zone 1 through line I6 and is directed through heat exchanger I1 and line IB into stripping zone I9. Zone I 9 preferably contains a'suitable packing material such `as carbon Raschig rings land/or contacting means such as bubble trays, side to side pans, etc. `In yzone I9 the caustic-methanol solution is subjected to regeneration by heating, which in the case here illustrated comprises reboiling of the solution in the lower portion of the stripping zone. It is understood that other suitable means `of supplying heat to the lower portion of this zone, such as by means of superheated steam, etc. may be employed. The temperature maintained in the lower portion of the stripping zone is substantially the boiling point of the caustic solution, which, with a 48 Baume sodium hydroxide solution, will be ofthe order of 285 F. The temperature at the top of the stripping zone may be of the order of 200 to 250 F. depending in part on the temperature of the spent treating solution introduced thereto through line I8.

As a result of the heating, the sodium mercaptides are decomposed to mercaptans, with the `liberation of an equivalent amount of sodium hydroxide. The sodium hydroxide is withdrawn from the lower portion of zone I9 through line 20, a portion thereof being recycled by Way of line 2I into and through reboiler 22 `and line 23 back to zone I9. Any suitable heating medium may be utilized in reboiler 22 in` order to furnish the heat required for regeneration of the causticmethanol solution. While all or a portion of the regenerated caustic solution may be withdrawn from the process through the extension of line 2l `as illustrated, preferably all or a portion of the caustic solution is directed through line 24, heat exchanger 25 and lines 26 and II to zone 1 for further use in the process. The mercaptans, methanol and Water are vaporized in zone I9 and `are directed therefrom through line 21, condenser 28 and line 29 into separator 30. The condensate is permitted to settle landstratify in separator 30, whereby there a mercaptan layer and a methanol-water layer are formed. In order to lassist in this separation, radditional water may be introduced by way of line 3| into 21. This water may conveniently comprise a portion of the water being withdrawn from the bottom of the methanol column in the manner to be hereinafter set forth.

The mercaptan fraction separated in zone 30 will contain varying lamounts of entrained hydrocarbons, depending upon the particular gasoline charging stock and the specific operating conditions employed in the process. The entrained hydrocarbons may range from 2% in an extreme case to as high Ias 50% or more of the mercaptan fraction. In addition, as hereinbefore set forth, the mercaptans comprise a chemical composition of .hydrocarbons and sulfur. In accordance with the present invention, the mercaptan fraction is withdrawn from zone 30 through line 32 and is subjected to a mercaptan-decomposition treatment, in a manner to be hereinafter set forth, in order to recover both chemically combined hydrocarbon portion of the mercaptan molecule and the hydrocarbon in physical admixture with the mercaptan. y

The methanol-water fraction is withdrawn from separator 30 through line 33 and is directed .into methanol column 34. In-,zone 34 the aqueous methanol fraction is subjected to heating and distillation by any suitable means. Heating may be accomplished by use of a reboiler arrangement as illustrated or by the introduction of superheated steam into the lower portion of zone 34, etc. In Zone 34, the methanol is separated from the water, and the latter is removed from the lower portion thereof through line 35. A portion of the Water is recycled through line 36, reboiler 31 and line 38 back to zone 34, while the remaining portion is withdrawn through the extension of line 35 as illustrated. When desired, a portion of this water may be supplied through line 3l into line 21 as hereinbefore Set forth or the water may be used to wash the treated gasoline being withdrawn through line I5, and the wash water may be returned to either caustic stripping Zone I 9 or methanol column 34. Methanol is removed from the upper portion of zone 34 through line 39 and is directed through condenser 40 and line 4I into receiver 42. The methanol is removed from receiver 42 through line 43, a portion thereof is recycled by way of line 44 to the upper portion of zone 34 to act as a cooling and refluxing medium therein, while the remaining portion may be removed from the process through the extension of line 43 as illustrated, but preferably is recycled at least in part through line 45 and I 4 to mercaptan extraction zone 1 for further use therein.

In accordance with the present invention the mercaptan fraction withdrawn from separator 30 through line 32 is subjected to a mercaptan decomposition treatment and, as hereinabove set forth, this treatment may take one of several forms. In one embodiment of the invention the mercaptan fraction comprises the sole charging stock to a high temperature treatment step and this accomplished by directing the mercaptan fraction through lines 32 and 46 into and through heater 41, wherein the mercaptan fraction is heatedto a temperature required to effect decomposition of the mercaptans into hydrogen sulfide and hydrocarbons. The heated products are then directed through line 48 and line 43 and through reactor 50, which may or may not contain a catalyst, and then are directed through line 5I to fractionator 52. In some cases, zone 5U may be omitted and the desired heating and reaction time obtained in the coils of heater 41, in which case the heated products are directed through lines 48 and 5I to fractionator 52.

In another embodiment of the invention the high temperature heating step may comprise a conventional catalytic or non-catalytic cracking, reforming or high temperature desulfurization process. Cracking and reforming operations are effected at a temperature of from about 800 F. to about 1000" F. High temperature desulfurization is effected at a temperature of above 500 F'. and generally of from about 650 to about 800n F. In this embodiment of the invention the crude oil, topped crude, gas oil, gasoline or other charge to the high temperature step of the process is introduced through line 53 and is directed, along with the mercaptan fraction being supplied by way of line 32, and 46 through heater 41 and the subsequent zones of the process. When hydrogen is to be employed, particularly in the case of reforming or high or low temperature desulfurization, it may be introduced to the process through line 54 or in any other suitable manner.

The separation to be effected in fractionator 52 will depend upon the particular type of process employed. When this process comprises a crack- 'ing operation, components boiling-higher than gasoline are separated from gasoline and lighter boiling components. The higher boilingcomponents are withdrawn from the lower portion of Zone 52 through line 55, a portion thereof being recycled by way of Vline 55, reboiler 51 and line 58 to zone 52, while the remaining portion may be withdrawn from the process through the extension .of line 55 or may be recycled by way of lines 59 and 45 for further conversion withinv the process. In this case, the overhead fraction withdrawn from fractionator 52 will comprise gasoline and lighter components and are directed through line S0, condenser 6! and line 62 to receiver 53. Normally gaseous components including hydrogen sulfide are removed from the process through line', while the gasoline is withdrawn from receiver 53 through line 55, a portion there- ,of being recycled by wayof line 56 to the upper portion of Zone'52 to serve as a cooling and refluxing medium therein. The gasoline being withdrawn through line will contain mercaptans formed during thehigh temperature conversion of the heavy charging stock introduced through line 53, and, in accordance with the present invention, is directed through line 61 for treatment in the caustic-methanol step ofY the process. Usually, the 'gasoline fraction will contain some hydrogen suliide and preferably the gasoline fraction is directed through lines 51 and l to pre- Wash zone 2. However, in some cases prewash Zone 2 may be omitted and the gasoline fraction may be directed through lines'l, 9 and E to mercaptan extraction zone 1.'

When desired, the gasoline fraction withdrawn Y through line 65 may be directed through line 68 to stabilizer 69, Wherefrom normally gaseous components including hydrogen sulfide are removed from the upper portion through line 10 and are directed through condenser 1| and line 12 to receiver 13. The uncondensed gases are Withdrawn from the process through line 14, While the condensate is withdrawn from receiver 13 through line 15, a portion being recycled by Way of line 15 to the upper portion of zone 69 to serve as a cooling and reuxing medium therein, While the remaining portion is withdrawn from the process through line 11. The gasoline separated in stabilizer Si) is withdrawn from thelower portion thereof through line 18, a portion thereof being recycled by way of line 19, reboiler 8U and line 3l to zone 69, and the remaining portion is Withdrawn from the process throughline 19 but preferaoly is supplied through lines 61 and I or lines 51 and 9 for further treatment within the process in the manner hereinbefore set forth. I n general, the stabilized gasoline will contain less hydrogen sulfide than the gasoline withdrawn from receiver 63 and, therefore, when the gasoline is free from hyrogen sulfide or'the hydrogen sulde content is sufficiently low, prewash zone 2 may be omitted.

When the charge to the high temperature step of the process comprises a gasoline and the mercaptan fraction from separator 30, separation in fractionator 52 will depend upon Whether any material boiling above the range of gasoline is formedv during the high temperature treating step. When such high boiling material is formed, the fractionator will function as hereinbefore described. On the other hand, when no high boiling components are present in the products supplied to zone 52, fractionation therein will be effected to separate normally gaseous components from gasoline boiling components, the former being withdrawn throughV line 60V from the upper portion of zone 52 and the gasoline components being withdrawn through line 55 from the lower' portion. In this case, the gasoline may be directed through lines 55 and 82 to line 61, to be supplied either through lines I or 9 for further treatment within the process.

In another embodiment of the invention, the gasolineV from thehigh temperature step of the process is supplied to the caustic-methanol treatment and the mercaptan fraction from separator 30 is supplied to thehigh temperature treatment. In this way the mercaptans are recycled to extinction; that is, the sulfur containing compounds are removed from the process only in the form of hydrogen sulfide, With the exception of the small amount of sulfur compounds which may be entrained in the other products of the process.

In certain cases mercaptans of the mixture from zone 30 may resist decomposition in the high temperature treatment and would eventually accumulate within the process. To meet this Vcontingency, line 83 is provided to WithdrawV stable mercaptans from the process. This is readily accomplished by withdrawing a bleed stream either continuously or periodically by Way of line 83.

It will thus be seen that the present invention provides for the recovery of hydrocarbons from the mercaptan fraction, which thereby improves the yields of desired hydrocarbons recovered from the process.

The following examples are introduced to illustrate further-the novelty and utility of the present invention but notwth the intention of unduly limiting the same. e

Example I A thermally cracked gasoline containing about 0.06% mercaptan sulfur is subjected to mercaptan extraction in the presence of an aqueous solution of 48 Baum caustic and methanol. The extraction zone is maintained at a temperature of about 100 F. and a pressure of '75`pounds per square inch. The spent caustic-methanol solution is heated to a temperature of about 210 F. by indirect heat exchange and is regenerated in the caustic stripping column, employing a temperature of about 285 F. in the lower portion of the stripping column. The mercaptan fraction withdrawn from separator 30 is supplied to a catalytic cracking process to which a gas oil charge is being supplied. vThe catalytic cracking is effected in the presence of a silica-alumina catalyst at a temperature of about 900 F. Hydrogen sulfide is separated from the catalytically cracked gasoline which also contains the hydrocarbonV components recovered from the mercaptans. Y A

In another operation,l thermally cracked gasoline is treated in the caustic-methanol process as hereinbefore set forth and the mercaptan fraction withdrawn from separator 30 Will contain approximately mercaptans and 25%hydrocarbons. The mercaptan fraction is supplied to a conventional thermal cracking process to which ytopped crude is charged. The thermalcracking is eiected in the absence of av catalyst a't a temperature of about 950 F. In the thermal cracking process, 60% of the mercaptans from receiver V3l] are converted into hydrogen sulde and hydrocarbons. The thermally.- cracked gasoline, containing hydrocarbons liberated from the mercaptan fraction, as well as 40% unconverted mercap- 75 tans from receiver30 and additional mercaptans formed in the cracking step, is recovered as a product from the thermal cracking step and is recycled to the caustic-methanol step, wherein the mercaptans are separated from the gasoline and are reco-vered in the mercaptan separator. The mercaptans are continuously recycled to the thermal cracking step and in this manner are substantially completely converted into hydrogen sulde and hydrocarbons.

I claim as my invention:

1. A combination process which comprises treating sour hydrocarbon oil with a caustic-solvent solution, separating from the treating step a mercaptan fraction, simultaneously subjecting a second hydrocarbon oil to a high temperature conversion treatment, supplying said mercaptan fraction to said high temperature treatment to form hydrogen sulfide and hydrocarbon therefrom, and supplying mercaptan-containing hydrocarbons from the high temperature treatment to the rst mentioned treating step.

2. The process of claim 1 further characterized in that said high temperature treatment comprises conversion of oil heavier than gasoline at a temperature of from about 800 to about 1000 F.

3. The process of claim 2 further characterized in that said high temperature treatment is effected in the presence of a cracking catalyst.

4. A combination process which comprises subjecting thermally cracked gasoline containing mercaptans to treatment With a caustic-methanol solution, recovering a mercaptan fraction from the products of the caustic-methanol treatment, commingling said mercaptan fraction with an oil heavier than gasoline and subjecting the mixture to conversion at a temperature of from about 800 to about 1000 F., in order to convert at least a portion of the inercaptans into hydrogen sulde and hydrocarbons and to convert the oil heavier than gasoline into gasoline components, separating a gasoline fraction containing mercaptans from the products of the last mentioned conversion, and supplying said gasoline fraction to treatment with caustic-methanol solution as aforesaid.

5. A combination process which comprises treating gasoline with a caustic-methanol solution, separating from said treating a mercaptan fraction, subjecting said mercaptan fraction in admixture with an oil heavier than gasoline to conversion in the presence of catalyst under conditions to convert at least a portion of the mercaptans into hydrogen sulfide and hydrocarbons and to produce gasoline from said heavier oil, separating hydrogen sulfide and a gasoline fraction from the resultant products, and recycling said Vgasoline fraction to treatment with causticmethanol solution as aforesaid.

6. The process of claim 5 further characterized in that the recycle of mercaptans within the .processis continued until substantially all the mercaptans are converted into other compounds.

7. A combination process in which cracked gasoline is subjected to treatment with causticmethanol solution to remove mercaptans, separating a mercaptan fraction from said treating,l

commingling said mercaptan jfraction with straight run gasoline and subjecting the mixture to high temperature treatment in the presence of a catalyst to convert mercaptans to hydrogen sulfide, separating a gasoline fraction and subjecting the same to treatment with causticmethanol as aforesaid.

8. A combination process which comprises treating gasoline with a caustic-methanol solution, separating from said treating a mercaptan fraction, subjecting said mercaptan fraction in admixture with another hydrocarbon oil to conversion in the presenceof hydrogen and a hydrgenation catalyst under conditions to convert atleast a portion of the mercaptans into hy`` drogen sulde and hydrocarbons, separating hydrogen sulfide and a gasoline fraction from the resultant products, and recycling said gasoline fraction to treatment with caustic-methanol solution as aforesaid 9. A combination lprocess which comprises treating sour hydrocarbon oil with an alkalisolvent solution, separating from the treating step a mercaptan fraction, simultaneously subjecting a second hydrocarbon oil to a high temperature conversion treatment, supplying said mercaptan fraction to said high temperature treatment to form hydrogen sulfide and hydrocarbon therefrom, and supplying mercaptancontaining hydrocarbons fromthe high temperature treatment tol the rst ,mentioned treating step.

A10. A combination process which comprises treating sour hydrocarbon oil with an alkali solution, separating from the treating step a mercaptan fraction, simultaneously subjecting a second hydrocarbon oil to ,a high temperature conversion treatment, supplying said mercaptan fraction to said high temperature treatment to form hydrogen sulde and hydrocarbon therefrom, and supplying mercaptan-containing hydrocarbons from the high temperature treatment to the first mentioned treating step. 1

11. A combination process which comprises treating sour hydrocarbon oil with a caustic solution, separating from the treating step a mercaptan fraction, simultaneously subjecting a second hydrocarbon oil to a high temperature conversion treatment, supplying said mercaptan fraction to said high temperature treatment to form hydrogen sulde and hydrocarbon therefrom, and supplying mercaptan-containing hydrocarbons from the high temperature treatment to the first mentioned treating step.

KENNETH M. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,043,254 Malisoff June 9, 1936` 2,324,927 Helman July 10,21943 2,447,529 Perkins Aug. 24, 1948 

1. A COMBINATION PROCESS WHICH COMPRISES TREATING SOUR HYDROCARBON OIL WITH A CAUSTIC-SOL VENT SOLUTION, SEPARATING FROM THE TREATING STEP A MERCAPTAN FRACTION, SIMULTANEOUSLY SUBJECTING A SECOND HYDROCARBON OIL TO A HIGH TEMPERATURE CONVERSION TREATMENT, SUPPLYING SAID MERCAPTAN FRACTION TO SAID HIGH TEMPERAURE TREATMENT TO FORM HYDROGEN SULFIDE AND HYDROCARBON THEREFROM, AND SUPPLYING MERCAPTAN-CONTAINING HYDROCARBONS FROM THE HIGH TEMPERATURE TREATMENT TO THE FIRST MENTIONED TREATING STEP. 